It was one of the most momentous weeks of Obama's presidency — a defining one for his administration's legacy.

"I do think it's been a significant morning, it's been a significant couple of days, and it's certainly been a significant month for not only the President and the administration, but for the country," Eric Schultz, the principal deputy White House press secretary, told reporters on Friday.

"And if you take a moment to step back, I think the developments we've all experienced over the past few days speak to not only the modern American presidency, but also speak to the reason this president ran for office."

Two milestones over the past three days will help shape the Obama legacy long after he leaves office:

After a brutal fight in Congress that he — and, curiously enough, Republican leaders — ended up winning, Obama is set to sign a bill that will give him so-called "fast-track" negotiating power on trade deals. His administration is in the process of negotiating the Trans-Pacific Partnership, a cornerstone of his "pivot" to Asia.

The Supreme Court ruled in favor of the Obama administration and upheld a key provision of the Affordable Care Act that allows the federal government to provide subsidies for health insurance to millions of low-income Americans. A ruling against the administration could have thrown the future of the law as Obama envisioned it into doubt.

And on Friday, the Supreme Court ruled that same-sex couples have a constitutional right to marriage, putting a feather in the cap of the first president who formally endorsed gay marriage smack dab in the middle of his re-election fight in 2012.

President Barack Obama and Vice President Joe Biden in the Rose Garden. Getty Images

The 'most important' piece for Obama's Asia pivot

Ian Bremmer, the president of Eurasia Group, told Business Insider that the Trans-Pacific Partnership is the "most important piece" of Obama's foreign-policy legacy.

"It's strengthening trade ties for 40% of the world's GDP; it's making good on US commitments to allies that are most interested in improving their relations with America; it's a net economic benefit for the US long term, and, by far most importantly, it's strategically important in countering China's efforts to build trade and financial architecture that completes with US-led global standards," Bremmer said.

"A failure on this front would have been a huge blow to the US in the most important part of the world for long-term American national interests."

Two weeks ago, it was basically left for dead. Obama endured a brutal fight with members of his own party on trade. He was rebuffed by House Minority Leader Nancy Pelosi (D-California) on a companion bill that needed to be paired with the fast-track authority for Obama to sign it.

Ultimately, House and Senate leaders worked around legislative setbacks and forced congressional Democrats into a corner. The fast-track authority passed the Senate Wednesday and headed to Obama's desk for his signature.

'Instrumental to the future of Obamacare'

The Supreme Court ruling on the Affordable Care Act could well end up being the most important event of the past week, as it entrenches Obamacare onto firm legal footing.

As Obama said in a victory-lap statement in the Rose Garden following the ruling, the law is "here to stay." And he nodded to the historic nature of the Affordable Care Act — the biggest federal healthcare overhaul in half a century.

"Three generations ago, we chose to end an era when seniors were left to languish in poverty," he said. "We passed Social Security, and slowly it was woven into the fabric of America and made a difference in the lives of millions of people. Two generations ago, we chose to end an age when Americans in their golden years didn't have the guarantee of health care. Medicare was passed, and it helped millions of people.

"This generation of Americans chose to finish the job."

The challenge, King v. Burwell, would have had the potential to cripple the law and throw its future into highly uncertain territory in the nearly three dozen states in which the federal government provides subsidies for low-income people to buy health insurance. Challengers argued that only states should have been able to hand out subsidies, pointing to four words in the law that say exchanges are to be "established by the state."

But the majority of Supreme Court justices — including conservative-leaning Chief Justice John Roberts — didn't buy the challengers' underlying theory. And in leaving no ambiguity in its decision, the high court prevented a future theoretical Republican administration from undoing the law executively. It'll take an act of Congress to weaken, much less repeal, the Affordable Care Act.

"The decision leaves no wiggle room for a future Administration that might have wanted to end the ACA's subsidies," said Larry Levitt, senior vice president at the Kaiser Family Foundation.

Justice 'arrives like a thunderbolt'

Not 24 hours later, Obama was back in the Rose Garden, delivering a statement on the Supreme Court's historic decision to legalize same-sex marriage nationwide. Justice, he said, had arrived "like a thunderbolt" and cemented a swift decade-plus of extraordinary shift on the issue from a gradually accepting American public.

He reflected on the often anonymous work of the people who "stood up," who came out, who "talked to parents," who endured bullying, who came to believe in themselves, and who "slowly made an entire country realize that love is love."

"What an extraordinary achievement," Obama said. "What a vindication of the belief that ordinary people can do extraordinary things. What a reminder of what Bobby Kennedy once said about how small actions can be like pebbles being thrown into a still lake, and ripples of hope cascade outwards and change the world."

Five hours and an Air Force One ride later, Obama delivered the eulogy for Clementa Pinckney, the reverend killed in last week's shooting in Charleston. He talked about some of the things — gun violence, racial relations, and more — that he thought ordinary people could change.

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